In a radio communication system, a radio base station generally transmits broadcast control data used to control communication with a radio terminal, more specifically, to establish and maintain radio communication. The broadcast control data is control data common to multiple radio terminals executing radio communication with the radio base station. Such broadcast control data is called MAP in WiMAX (IEEE802.16) that is a kind of radio communication system, for example, and includes data indicating an allocation result of communication channels used to transmit and receive communication data other than the broadcast control data.
In recent years, there has been widely used a radio base station configured to execute beam-forming-transmission using multiple antennas to improve communication quality in the radio communication system. The beam-forming-transmission is a control to direct a directional beam (a region with a strong electric field distribution) in a specific direction. The beam-forming-transmission allows even a radio terminal with degraded quality of communication with a radio base station (hereinafter referred to as a degraded radio terminal), such as a radio terminal located around a cell fringe, for example, to more reliably receive communication data from the radio base station.
Further, there has been proposed a method for a radio base station to diversity-transmit broadcast control data (see Patent Document 1). To be more specific, the radio base station described in Patent Document 1 transmits the broadcast control data by using a directionality pattern for directing a directional beam in predetermined multiple directions, regardless of a location of a radio terminal. Further, the radio base station uses a different directionality pattern every time it transmits the broadcast control data, thereby producing spatial and temporal diversity effects and thus improving the probability that a degraded radio terminal can normally receive the broadcast control data.